Rolling mill control system

ABSTRACT

A control system for the length of workpiece between stands in a multi-stand rolling mill combines a thickness signal, a width signal and a speed signal for each stand to provide a signal representing the rate of material volume going through the stand. This signal is then compared with the desired rate for each stand and the roll speed for that stand corrected accordingly. Adjustments are made for slippage and workpiece grow-back.

United States Patent Frostick Mar. 26, 1974 [54] ROLLING MILL CONTROL SYSTEM 3,688,532 9/1972 Silva 72/16 Inventor: Ha old G. Frostick North Strabane 3,332,263 7/1967 Beadle et al. 72/8 Townshp' washmgton County Primary Examiner--Milton S. Mehr [73] Assignee: United States Steel Corporation, Attorney, Agent, or Firm-Rea C. Helm Pittsburgh, Pa. 22 Filed: Feb. 2, 1973 [57] ABSTRACT A control system for the length of workpiece between stands in a multi-stand rolling mill combines a thickness signal, a width signal and a speed signal for each [52] US. Cl. 72/8, 72/20 stand to provide a signal representing the rate of mate- [51] Int. Cl B21b 37/00 ri l olume going through h n This signal is then [58] Field of Search 72/6-12, 16 compared with the desired rate for each stand and the roll speed for that stand corrected accordingly. Ad- [56] References Cited justments are made for slippage and workpiece grow- UNITED STATES PATENTS back' 2,287,851 6/1942 Zeitlin 72/9 Claims, 2 Drawing Figures 20 l 24 2a 4 I RaLL L040 RaLL LOAD RoLL LOAD GAP cELLs M GAP cELLs M GAP cELLs M SPEED sPEEo A sPEEo c0MPUTER CON TRaL- COMPUTER c0MTROL- COMPUTER c0/vTROL- LER LE1? LE1? I02 75 i 7a 66 6 2 6Q K 1 ROLLING MILL CONTROL SYSTEM This invention relates to a rolling mill control system and more particularly, to a control system for maintaining a desired workpiece length between stands in a mu]- ti-stand close-coupled steel rolling mill.

In some types of rolling on multi-stand rolling mills, it is desirable to develop tension to stretch the workpiece between stands. In other types of rolling, compression or substantially zero tension, may be desirable. In all multi-stand rolling whether in open pass or close pass roll arrangements or whether the workpiece is in tension, compression or neither, the length of the workpiece between stands is related to the distance between stands. This length is sometimes regulated by inducing a loop in the workpiece between stands to avoid undesirable tensions. Interstand tensioning devices are also used to regulate the length between stands. In closecoupled mills handling product with sufficient crosssection to withstand some degress of tension or compression, an approximate speed match of adjoining roll stands has been generally accepted as satisfactory.

Close-coupled mills minimize heat loss in the product because of the close spacing. This results in less scale formation and a more uniform product because the temperature run down is minimized. Close-coupled mills reduce space requirements and also reduce power requirements because of minimal heat loss in the workpiece.

In accordance with my invention, electrical signals representing width, thickness and speed of the material in each pass of a rolling mill are combined in a computer to determine the rate of material volume going through the pass. The rate is compared to the desired rate and the speed of the mill corrected, if necessary, to the desired rate. The process is repeated for each pass. Adjustments are made for slippage caused by temperature, surface conditions, steel texture, lubricants, friction, temperature run down, coolant distortions and workpiece grow-back.

It is therefore an object of my invention to provide a multi-stand rolling mill control system which controls the length of the workpiece between stands.

Another object is to provide a control system in which the workpiece is substantially free of tension or compression between stands.

Still another object is to provide a control system which maintains a uniform volume of workpiece per unit time through each stand.

These and other objects will become more apparent after referring to the following specification and drawing in which:

FIG. 1 is a schematic drawing of the preferred embodiment of the control system of my invention connected to a close-coupled rolling mill; and

FIG. 2 is a partial schematic diagram illustrating alternative embodiments.

Referring now -to FIG. 1, reference numeral 2 indicates the work rolls of the first stand of a rolling mill rolling a steel slab S in the direction of the arrow and a second pair of work rolls 4 of the second stand, here shown as edge rolls, closely coupled to the first stand. A third set of work rolls 6 of a third stand are closely coupled to the second stand and arranged for further thickness reduction of slab S. This is a conventional arrangement of a close-coupled mill, although there may be more stands, and they may not include both horizontal and vertical work rolls.

A first motor 8 drives work rolls 2 and is controlled by a first speed controller 10; a second motor 12 drives rolls 4 and is controlled by a second speed controller 14; a third motor 16 drives rolls 6 and is controlled by a third speed controller 18. A first roll gap measuring device 20, such as the type described in De Caro et al. US. Pat. No. 3,358,485 is connected to rolls 2 to provide a signal 22 which is a measure of the gap between rolls 2. A second similar signal roll gap measuring device 24 provides an output signal 26 which is a measure of the gap between rolls 4. A third similar roll gap measuring device 28 provides an output signal 30 which is a measure of the gap between rolls 6. A first set of load cells 32 is arranged in the housing (not shown) of the first stand to provide an output signal 34 which is a measure of the pressure on the workpiece between rolls 2 and therefore a measure of the forward slip..Signal 34 is connected to the first input of controller 10. A second set of load cells 36 provides a signal 38 which is a measure of the pressure between rolls 4 and therefore a measure of the forward slip. Signal 38 is connected to the first input of controller 14. A third set of load cells 40 provides a signal 42 which is a measure of the pressure between rolls 6 and therefore a measure of the forward slip. Signal 42 is connected to the first input of controller 18. A first tachometer generator 44 is connected to rolls 2 andprovides a first roll speed signal 46 for rolls 2. A second tachometer generator 48 provides a second roll speed signal 50 for rolls 4, and a third tachometer generator 52 provides a third roll speed signal 54for rolls 8. Roll speed signals 46, 50 and 54 are in terms of unit distance per unit of time..

- A width reference potentiometer 56 provides a width signal 58 to the first input of a computer 60.which may be a Westinghouse-Type Prodac 2,000 computer. Signals22 and 46 provide the second and third inputs of computer 60. Signal 22 is also connected to a first input of a second computer 62 of the same type as computer 60. A first gap bias potentiometer 64 provides a first gap bias signal 66 which is connected to the second input of computer 62. Signals 26 and 50 provide the third and fourth inputs of computer 62. Signal 26 is also connected to a first input of a third computer 68 of the same type as computers 60 and 62. A second gap bias potentiometer 70 provides a second gap bias signal 72 which is connected to the second input of computer 68.

Signals 30 and 54 provide the third and fourth inputs of computer 68.

Computer 60 has an output signal 74, a first corrected motor speed signal, which is connected to the second input of controller 10. A desired motor speed reference potentiometer 76 has an output 78 connected to the fourth input of computer 60. A first slip bias reference potentiometer 80 provides a first slip bias speed signal 82.to a third input of controller 10. Controller 10 provides a first adjusted motor speed signal 84 to motor 8 and to a fifth input of computer 62.

Computer 62 has an output signal 86, a second corrected motor speed signal, which is connected to the second input of controller 14. A second slip bias reference potentiometer 88 provides a second slip bias speed signal 90 to a third input of controller 14. Controller 14 provides a second adjusted motor speed signal 92 to motor 12 and to a fifth input of computer 68. Computer 68 has an output signal 94, a third corrected motor speed signal, which is connected to the second input of controller 18. A third slip bias reference potentiometer 96 provides a third slip bias speed signal 98 to a third input of controller 18. Controller 18 provides a third adjusted motor speed signal 100 to motor 16.

in the operation of my control system, the various potentiometers are first set to desired values. Potentiometer 56 is set to provide signal 58 which is representative of the width of slab S before it enters rolls 2. Potentiometer 76 is set to provide signal 78 which is representative of thedesired rolling rate expressed as a volume of material passing through rolls 2 in a unit of time. Potentiometer 64 is set to provide a signal 66 which adjusts the roll gap signal 22 in computer 62 to compensate for the workpiece grow-back that occurs after the slab S leaves rolls 2. In a similar manner potentiometer 70 is set to compensate for the workpiece grow-back after the slab S leaves rolls 4. Potentiometer 80 is set-to provide signal 82 to place the workpiece under compression or tension between rolls 2 and 4 if desired. In addition, potentiometer 80 is set to compensate for any slippage caused by temperature, surface conditions, steel texture, lubricants, friction, workpiece temperature run down, and the coolant distortions. Potentiometer 88 is set in the same manner with respect to rolls 4 and potentiometer 96 for rolls 6.

When the rolling of slab S begins, computer 60 is supplied a roll speed signal 46 from tachometer generator 44, a roll gap signal 22 from roll gap measuring device 20, and a width signal 58 from potentiometer 56. Com- I puter 60 multiplies these three signals together and compares the results, expressed in terms the rate of volume of material S actually passing through rolls.2 per unit of time, to thedesired rate from signal 78 to provide a rate error. The error is used to correct the desired rate signal which becomes the correctedmotor speed signal 74.

Controller 10 then combines signals 34, 74, and 82 to provide the adjusted motor speed signal 84 to control the speed of motor 8 and to provide the signal representative of the desired rolling rate for computer 62. Load cells 32 measure the roll separating force which is proportional to the adjustments required for stand stretch, roll flattening, roll deflection and forward slip.

The speed of edge rolls 4 is controlled in a similar manner. One dimension of the slab is determined from signal 22, the roll gap of-the previous stand. Signal 22 is adjusted for workpiece grow-back by signal 66 in computer 62. The other dimension of slab S is determined by a second roll gap determining device 24 providing a signal 26 to computer 62. Tachometer generator 48 provides the roll speed signal 50. Computer 62 multiplies adjusted signal 22, signal 26 and signal 50 together, compares the results with signal 84 and provides corrected motor speed signal 86 in the same manner that signal 74 was provided by computer 60. Controller 14 then combines signals 38, 86 and 90 to provide adjusted motor speed signal 92 in the same manner that signal 84 was developed by controller 10.

The speed of rolls 6 is controlled by signal. 100 developed in a manner similar to signals 84 and 92. if the rolling mill contains more than three stands, the control system components are repeated for each stand. Thus a signal representative of the desired rolling rate for the next stand would be provided at 102 and a dimension signal for the next stand would bev provided at 104. The

functions of computers 60, 62 and 68 and any other computers could be performedby a single computer.

Thus, I have provided a control system which adjusts the speed of each stand to rollan equal volume per unit time for each stand thereby maintaining the length of the workpiece between the stands to the distance be tween stands. in addition, provisions are made for establishing desired levels of tension or compression of the workpiece between stands if desired.

While the preferred embodiment of my invention is shown with a first set of horizontal rolls, a second set of vertical rolls, and a third set of horizontal rolls, this arrangement is intended to illustrate how such a roll arrangement would be connected. If the axes of the rolls are parallel to the axes of the immediately preceding rolls, the control system is altered slightly as shown in FIG. 2, where width signal 58 and a width adjustment signal 106 from a potentiometer 108 are connected to computer 62. Potentiometer 108 is'set to adjust for any width spread of the workpiece as it passes through rolls 2. Signal 58 may be connected to computers of subsequent stands at 110.

While roll gap measuring devices 20, 24, and 28 have been described as illustrated in De Caro et al. U.S. Pat. No. 3,358,485, any conventional gauge, such as an X-ray gauge or a back-lighted gauge 112 (FIG. 2), could be used vto supply a dimension signal for signal While several embodiments of my invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim: v

1. Apparatus for'controlling the length of a workpiece between stands in a rolling mill which comprises a variable speed motor connected to drive the rolls of each stand; a motor controller connected to each motor for controlling the speed of each motor; means connected to each stand for providing a first signal representative of the thickness of the workpiece as it' emerges from the work rolls of the stand; means connected to each stand for providing a second signal representative of the width of the workpiece as it emerges from the work rolls of the stand; means connected to each stand'for providing a third signal representative of the speed of the workpiece as it emerges from the work rolls of the stand; means for providing a fourth signal representative of the desired rate of material flow through each stand and computing means for each stand connected to the motor controller and the means for providing the first, second, third and fourth signals for that stand for providing a signal representative of the actual rate of material flow through that stand by combining said first, second and third signals, for providing an error rate signal by comparing the signal rep- 7 resentative of the actual rate of material flow to the fourth signal and for providing a corrected motor speed signal for the motor controller of that stand by combining the error rate signal and the fourth signal.

2. Apparatus according to claim 1 in which the axes of the work rolls of one sta'nd are essentially perpendicular to the axes of the work rolls of the next stand, the-- means for providing a second signal for the first stand is a first potentiometer and the means for providing a second signal for each subsequent stand includes the means for providing a first signal for the next prior stand and means for adjusting the first signal for the next prior stand for workpiece grow-back.

3. Apparatus according to claim 2 in which the means for providing a fourth signal for the first stand is a second potentiometer and the fourth signal for each subsequent stand is the motor speed signal for the next prior stand and which includes means connected to the motor controller for adjusting the corrected motor speed signal for the forward slip of each stand andfor adjusting the workpiece tension between stands.

4. Apparatus according to claim 3 in which the means for providing a third signal for each stand includes a tachometer generator connected to the work rolls of each stand and the means for providing a first signal for each stand includes means for measuring the gap between the work rolls of each stand.

5. Apparatus according to claim 4 in which the means for adjusting for the forward slip of each stand includes load cells mounted on the roll housings of each stand for measuring the pressure of the rolls on the workpiece.

6. Apparatus according to claim 1 in which the axes of the work rolls of all stands are essentially parallel to each other, the means for providing a second signal for the first stand includes a third potentiometer and the means for providing a second signal for each subsequent stand includes said third potentiometer and means connected to the third potentiometer for adjusting the second signal for the first stand for expected width spread from passage through work rolls.

7. Apparatus according to claim 6 in which the means for providing a fourth signal for the first stand is a fourth potentiometer and the fourth signal for each subsequent stand is the motor speed signal for the next prior stand and which includes means connected to the motor controller for adjusting the corrected motor speed signal for the forward slip of each stand and for adjusting the workpiece tension between stands.

8. Apparatus according to claim 7 in which the means for providing a third signal for each stand includes a tachometer generator connected to the work rolls of each stand and the means for providing a first signal for each stand includes means for measuring the gap between the work rolls of each stand.

9. Apparatus according to claim 8 in which the means for adjusting for the forward slip of each stand includes load cells mounted on the roll housings of each stand for measuring the pressure of the rolls on the workpiece.

10. Apparatus according to claim 8 in which the means for providing a first signal for each stand includes a conventional thickness gauge. 

1. Apparatus for controlling the length of a workpiece between stands in a rolling mill which comprises a variable speed motor connected to drive the rolls of each stand; a motor controller connected to each motor for controlling the speed of each motor; means connected to each stand for providing a first signal representative of the thickness of the workpiece as it emerges from the work rolls of the stand; means connected to each stand for providing a second signal representative of the width of the workpiece as it emerges from the work rolls of the stand; means connected to each stand for providing a third signal representative of the speed of the workpiece as it emerges from the work rolls of the stand; means for providing a fourth signal representative of the desired rate of material flow through each stand and computing means for each stand connected to the motor controller and the means for providing the first, second, third and fourth signals for that stand for providing a signal representative of the actual rate of material flow through that stand by combining said first, second and third signals, for providing an error rate signal by comparing the signal representative of the actual rate of material flow to the fourth signal and for providing a corrected motor speed signal for the motor controller of that stand by combining the error rate signal and the fourth signal.
 2. Apparatus according to claim 1 in which the axes of the work rolls of one stand are essentially perpendicular to the axes of the work rolls of the next stand, the means for providing a second signal for the first stand is a first potentiometer and the means for providing a second signal for each subsequent stand includes the means for providing a first signal for the next prior stand and means for adjusting the first signal for the next prior stand for workpiece grow-back.
 3. Apparatus according to claim 2 in which the means for providing a fourth signal for the first stand is a second potentiometer and the fourth signal for each subsequent stand is the motor speed signal for the next prior stand and which includes means connected to the motor controller for adjusting the corrected motor speed signal for the forward slip of each stand and for adjusting the workpiece tension between stands.
 4. Apparatus according to claim 3 in which the means for providing a third signal for each stand includes a tachometer generator connected to the work rolls of each stand and the means for providing a first signal for each stand includes means for measuring the gap between the work rolls of each stand.
 5. Apparatus according to claim 4 in which the means for adjusting for the forward slip of each stand includes load cells mounted on the roll housings of each stand for measuring the pressure of the rolls on the workpiece.
 6. Apparatus according to claim 1 in which the axes of the work rolls of all stands are essentially parallel to each otHer, the means for providing a second signal for the first stand includes a third potentiometer and the means for providing a second signal for each subsequent stand includes said third potentiometer and means connected to the third potentiometer for adjusting the second signal for the first stand for expected width spread from passage through work rolls.
 7. Apparatus according to claim 6 in which the means for providing a fourth signal for the first stand is a fourth potentiometer and the fourth signal for each subsequent stand is the motor speed signal for the next prior stand and which includes means connected to the motor controller for adjusting the corrected motor speed signal for the forward slip of each stand and for adjusting the workpiece tension between stands.
 8. Apparatus according to claim 7 in which the means for providing a third signal for each stand includes a tachometer generator connected to the work rolls of each stand and the means for providing a first signal for each stand includes means for measuring the gap between the work rolls of each stand.
 9. Apparatus according to claim 8 in which the means for adjusting for the forward slip of each stand includes load cells mounted on the roll housings of each stand for measuring the pressure of the rolls on the workpiece.
 10. Apparatus according to claim 8 in which the means for providing a first signal for each stand includes a conventional thickness gauge. 